linux-kernel - Re: [PATCH 1/2] i2c: designware: Avoid taking clk

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Message-ID: <aKX4xEYE29JC_g14@xhacker>
Date: Thu, 21 Aug 2025 00:33:08 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Jan Dabros <jsd@...ihalf.com>, Andi Shyti <andi.shyti@...nel.org>,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 1/2] i2c: designware: Avoid taking clk_prepare mutex in
 PM callbacks

On Wed, Aug 20, 2025 at 07:05:42PM +0300, Andy Shevchenko wrote:
> On Wed, Aug 20, 2025 at 11:31:24PM +0800, Jisheng Zhang wrote:
> > This is unsafe, as the runtime PM callbacks are called from the PM
> > workqueue, so this may deadlock when handling an i2c attached clock,
> > which may already hold the clk_prepare mutex from another context.
> 
> Can you be more specific? What is the actual issue in practice?
> Do you have traces and lockdep warnings?

Assume we use i2c designware to control any i2c based clks, e.g the
clk-si5351.c driver. In its .clk_prepare, we'll get the prepare_lock
mutex, then we call i2c adapter to operate the regs, to runtime resume
the i2c adapter, we call clk_prepare_enable() which will try to get
the prepare_lock mutex again.

Regards.

> 
> AFAICS it seems related to the bus recovery mechanism. Is this what you have in
> mind?
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>